After manufacturing, a contact lens can interact with its packaging during storage or shipment. Efforts have been made by various entities to reduce these interactions. In general the minimization of lens-to-package interaction should be optimized. In some situations, it is suspected that there may be instances where the lens becomes folded (or at least slightly folded) during storage, even if unfolded when placed on the eye. Depending on the type of lens material, the effect of such folding could range from a handling inconvenience to an effect on the lens optical properties.
After reviewing this condition, the inventors have successfully created a “low head space” condition for the lens in the package, while retaining high manufacturing efficiency in areas related to yield, throughput and capital employed. In other words, it is felt that providing for minimal space (i.e., “low” “head space”) between the lens and the cover of the package would be beneficial to reduce the possibility of lens folding or inverting (that is, the lens flipping over.
The parameters involved in the project to provide “low head space” are:
Conservation of lens design—lens interaction with the packaging post-manufacturing should be minimized.
Customer experience—any negative customer experience should be avoided.
Sterility—the sterility barrier (namely the heat seal between the foil and package) should be considered, both on the manufacturing line and during shipment.
The following terms will be used:
Dimpled package. The term “dimpled package” refers to the action of putting a concave shape in the foil of the package so that the plane of the foil projects inwards from the plane of the heat seal ring which joins the foil to the package. This reduces the head space available in the package at a given solution dose volume.Dimple. When a part in the middle of the heat seal die that pushed onto the foil as the die affixes the foil to the package, the resultant concavity is referred to as a “dimple”.Sag refers to the distance between the plane defined by the top of the heat seal ring and the apex of the dimple.Displacement refers to the volume displaced due to the shape of the dimple, from the reference plane defined by the top of the heat seal ring.Inside Diameter, or ID, or Diameter refers to the outside diameter of the dimple, where it meets the plane defined by the top of the heat seal ring.Outside Diameter or OD refers to the outermost diameter of the dimple. It may be different from the ID when the dimple has a flange with a diameter greater that the ID.Mounting features refers to the design feature that allows the dimple to be secured in the heat seal die.Pattern or emboss refers to a shape on the foil which forms the dimple, that does not alter the main concave form.